Methods and apparatus for controlling catalytic processes, including the deposition of carbon based particles

ABSTRACT

Methods and apparatus for controlling a catalytic layer deposition process are provided. A feed stream comprising a carbon source is provided to a catalyst layer. An asymmetrical alternating current is applied to the catalyst layer. A polarization impedance of the catalyst layer is monitored. The polarization impedance can be controlled by varying the asymmetrical alternating current. The controlling of the polarization impedance provides control over the structure and amount of carbon particles deposited on the catalyst layer. The carbon particles may be in the form of nanotubes, fullerenes, and/or nanoparticles.

This application is a continuation-in-part of commonly-owned U.S. patentapplication Ser. No. 11/588,113 entitled “Methods and Apparatus forControlling Catalytic Processes, Including Catalyst Regeneration andSoot Elimination” filed on Oct. 25, 2006, and also claims the benefit ofU.S. provisional patent application No. 61/127,377 filed on May 12,2008, each of which is incorporated herein and made a part hereof byreference for all purposes as if set forth in its entirety.

U.S. patent application Ser. No. 11/588,113 is a continuation-in-part ofcommonly owned U.S. patent application Ser. No. 10/423,376 filed on Apr.25, 2003 (now U.S. Pat. No. 7,325,392, issued on Feb. 5, 2008), and alsoclaims the benefit of U.S. provisional patent application No. 60/731,570filed on Oct. 28, 2005.

BACKGROUND OF THE INVENTION

The present invention relates generally to catalytic processes. Moreparticularly, the present invention provides methods and apparatus forcontrolling a catalytic layer deposition process, including thedeposition of carbon based materials in the form of nanotubes orfullerenes.

Catalyst systems are employed extensively to reform light hydrocarbonstreams, i.e. reduce methane and other light hydrocarbons to hydrogen,and to remediate exhaust streams, including reducing and/or oxidizinginternal combustion engine exhaust to innocuous compounds.

A problem encountered with prior art catalyst systems is poisoning ofthe catalyst. One source of such poisoning is theadsorption/infiltration of oxygen-containing species such as carbonmonoxide. Carbon monoxide interferes with the catalysis mechanism.Another source of poisoning is the deposition of carbon.

Methods of addressing catalyst poisoning include applying to thecatalyst a direct current (DC) electric field and/or heating it to anelevated temperature, i.e. about 300° C. to about 800° C. Most commonly,an electric field and heat are concurrently applied. Application of a DCelectric field and heat expels or pumps oxygen-containing molecularspecies from the catalyst. Examples of the prior art application of DCcurrent and/or heat to a catalyst are described in the following: U.S.Pat./application Nos. 2001/0000889; 2002/0045076; 4,318,708; 5,006,425;5,232,882; 6,214,195; and 6,267,864.

For example, it is known that the yield of the catalytic processes canbe increased (enhanced) by the polarization of the catalytic interfacesunder certain conditions. The overall voltages applied are low (up to1-2 V), but they are applied across interfaces which are very thin(e.g., the thickness of the interface is on the order of magnitude of ˜1nanometer, which is close to the diameter of a small molecule). Thisleads to the creation of very high electric fields across the polarizedinterfaces: the order of magnitude of these fields can be as high as 10⁶V/cm or more. Such high fields polarize (excite) the molecules of thesubstances that react in the catalytic system, and can pump ions acrossthe interface. The result of these processes is that under controlledconditions, the concentration and the activity of catalytic sitesavailable for the reaction increases beyond the concentration that wasdetermined by the preparation process of the catalyst. This process isknown in the prior art as the NEMCA (Nonfaradaic ElectrochemicalModification of Catalytic Activity) effect. However, the enhancement ofthe catalytic activity achieved by the NEMCA effect is very difficult tocontrol.

One problem encountered with application of a DC electric field tocatalyst systems is a lack of a means for monitoring and sensing thelevel of poisoning present in the catalyst in real time or on acontinuous basis. This lack of means to monitor and sense the level ofpoisoning in the catalyst in real time hinders precise and timelyapplication of the DC electric fields. Precise and timely application ofDC electric field is important because if the field is too weak, therate of expulsion of oxygen-containing species may be too low and suchspecies may accumulate. If the DC field is too strong, the incidence ofcatalytically effective sites in the catalyst may be reduced.

The application of heat to catalyst systems also has the problem of alack of real time control means, and also suffers from imprecise effectsof temperature on catalyst behavior and the physical structure of thecatalyst system. If the temperature of the catalyst is too low, thecatalyst may become fouled (dirty) and the kinetics of the catalyzedreaction may be negatively altered. If the temperature is too high, thekinetics of the catalyzed reaction may be negatively altered and/or themicrostructure of the catalyst may be destroyed.

Nanotubes are used in an ever increasing number of commercialapplications (e.g., composite materials, catalysts, structural materialsfor medical use, structural materials in the defense and avionicsindustries, electronic devices, electrochemical devices (e.g., batteryelectrodes and sensors), hydrogen storage, and the like). It is alsowell-known to produce carbon nanotubes and/or fullerenes in bulk usingvarious methods, such as electrochemical techniques (as disclosed forexample in Zhou, et al, “Synthesis of Carbon Nanotubes ByElectrochemical Deposition at Room Temperature” Carbon 44 (2006)1013-1024), arc evaporation, sputtering, Chemical Vapor Deposition (CVD)and Plasma Enhanced Chemical Vapor Deposition (PECVD). The yieldsachieved with these methods are fairly low, hence the price of materialswith well-defined characteristics can be very high, reaching more than$20,000/gram for some types. To the best of applicant's knowledge, todate there has not been a control process which enables a high yield atlow cost while at the same time providing control over thecharacteristics and structure of the carbon nanotubes.

It would be advantageous to provide an active catalytic process,including an active catalytic layer deposition process, as opposed tothe passive nature of prior art catalytic processes.

It would be further advantageous to provide a simple, real time way tocontrol the enhancement of catalytic reactions and the deposition of afullerene/nanotube layer.

It would be still further advantageous not only to enhance the oxidationreactions in the catalyst, but also to oxidize carbon particles (soot)to CO and subsequently to CO₂, resulting in a drastic decrease (andpossibly complete elimination) of soot particles from the diesel exhaustgases and also to regenerate the catalyst.

It would also be advantageous to control the catalytic reaction in orderto control the characteristics of a layer deposited on the catalyst. Inparticular, it would be advantageous to control the catalytic reactionso that carbon-based materials are deposited on the catalyst layer inthe form of carbon nanotubes and/or fullerenes, and to enable removal ofthe carbon nanotubes/fullerenes for use in a wide variety of commercialapplications.

The methods, apparatus, and systems of the present invention provide theforegoing and other advantages.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for controlling acatalytic layer deposition process, including the deposition of carbonbased materials in the form of nanotubes, fullerenes, and/ornanoparticles.

In one example embodiment of the present invention, a method forcontrolling a catalytic layer deposition process is provided. The methodcomprises providing a feed stream comprising a carbon source to acatalyst layer, providing an asymmetrical alternating current to thecatalyst layer, monitoring a polarization impedance of the catalystlayer, and controlling the polarization impedance by varying theasymmetrical alternating current. The controlling of the polarizationimpedance provides control over the structure and amount of carbonparticles deposited on the catalyst layer.

The controlling of the polarization impedance may further comprisecorrelating a time variation of the polarization with at least one of athickness and the structure of the deposited carbon particles on thecatalyst layer. Measured polarization impedance values from themonitoring may be correlated to a database linking each of thepolarization impedance values with data regarding at least one of thechemical nature, structure and average value for ratios of depositvolume/unit of surface area.

In a further example embodiment, the method may further compriseapplying a carrier gas containing oxygen to the catalyst layer,monitoring a partial pressure of oxygen in the carrier gas at thecatalyst layer, and adjusting the polarization impedance based on themonitoring of the partial pressure of oxygen in order to enhance thedeposition of the carbon particles on the catalyst layer.

The catalyst layer may be supported on or in close contact with a solidelectrolyte. An ionic conductivity of the solid electrolyte may bewithin a range of between approximately 1 to 10⁻⁴ ohm⁻¹*cm⁻¹. Thecatalyst layer may comprise one of platinum, a semiconducting oxide, asemiconducting materials, or the like. The solid electrolyte maycomprise one of stabilized zirconia, stabilized bismuth oxide, forms ofbeta alumina, Nafion, a mixed conductor, or the like.

The carbon deposits may comprise at least one of nanotubes, fullerenes,and nanoparticles. The method may further comprise harvesting the atleast one of nanotubes, fullerenes, and nanoparticles from the depositedcarbon particles.

At least one of an amplitude and a phase of the asymmetrical alternatingcurrent may be varied in order to regenerate the catalyst layersubsequent to the harvesting.

The carbon source may comprise at least one of CO, CO₂, hydrocarbons,oxygenated hydrocarbon-derivatives, organic compounds, and the like. Thefeed stream may comprise one of water or steam.

The method may also include one of extracting or electrically pumpingoxygen from the catalyst layer to generate a reduction reaction forinitiating or enhancing the deposition of the carbon particles onto thecatalyst layer.

The deposition of the carbon particles on the catalyst layer may bemonitored. Monitoring of the deposition of the carbon particles maycomprise monitoring a rate or structure of the carbon particlesdeposited on the catalyst layer. Alternatively, the monitoring of thedeposition of the carbon particles may comprise monitoring at least oneparameter which describes an interfacial impedance of the catalystlayer, and determining an amount of the carbon particles deposited onthe catalyst layer as a function of values of the at least one monitoredparameter. The at least one monitored parameter may comprise at leastone of the monitored polarization impedance and a phase angle of theinterfacial impedance.

The method may further comprise varying at least one of an amplitude anda phase of the asymmetrical alternating current in order to controlcharacteristics of the deposited layer. The at least one of theamplitude and the phase of the asymmetrical alternating current may bevaried to bring the polarization impedance to a value within apredetermined range of values when the polarization impedance valuefalls outside of the predetermined range. The predetermined range may bea range of values around an original polarization impedance value of thecatalyst layer prior to use. At least one of the amplitude and the phaseof the asymmetrical alternating current may be varied to achieve a phaseangle of an interfacial impedance of the catalyst layer which is withina range of between approximately −10 degrees and +10 degrees.

In a further example embodiment, at least one of water, steam, oxygen,and heat may be applied to the catalyst layer. The application of the atleast one of the water, steam, oxygen, and heat may be controlled inorder to control the deposition of the carbon particles on the catalystlayer.

A carrier gas containing oxygen may be applied to the catalyst layer.The partial pressure of oxygen in the carrier gas may be controlled inorder to enhance the deposition of the carbon particles on the catalystlayer.

In one example embodiment, the feed stream may comprise at least one ofa liquid phase and a gas phase. The method may further comprise at leastone of (a) varying at least one of a phase and an amplitude of thealternating current, and (b) controlling at least one of an amount ofwater, steam, and oxygen applied to the catalyst layer or to a depositedlayer formed by the deposition of the carbon particles in order toprovide at least one of (i) a reduction of the at least one of theliquid phase and gas phase in contact with the catalyst layer, and (ii)stimulate growth of the deposited layer. Further, an amount of heatapplied to the catalyst layer may be controlled in order to furthercontrol at least one of the structure and a thickness of the depositedcarbon particles on the catalyst layer.

The present invention includes a further method for controlling acatalytic layer deposition process. The method comprises providing afeed stream to a catalyst layer, the feed stream comprising at least oneof carbon, silicon, doped silicon, silicon carbide, gallium arsenide,niobium, and boron (or the like). An asymmetrical alternating current isapplied to the catalyst layer and a polarization impedance of thecatalyst layer is monitored. The polarization impedance may becontrolled by varying the asymmetrical alternating current. A depositionlayer is formed on the catalyst layer as a function of the controllingof the polarization impedance. The deposition layer may comprise atleast one of nanotubes, fullerenes, and nanoparticles.

The present invention also includes apparatus for controlling acatalytic layer deposition process corresponding to the above-describedmethods. For example, the present invention includes an apparatus forcontrolling a catalytic layer deposition process which comprises meansfor providing a feed stream comprising a carbon source to a catalystlayer, means for providing an asymmetrical alternating current to thecatalyst layer, means for monitoring a polarization impedance of thecatalyst layer, and means for controlling the polarization impedance byvarying the asymmetrical alternating current. The controlling of thepolarization impedance provides control over the structure and amount ofcarbon particles deposited on the catalyst layer.

The apparatus may include additional features of the methods describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe appended drawing figures, wherein like reference numerals denotelike elements, and:

FIG. 1 (FIGS. 1 a and 1 b) shows the known formation of partiallyblocking oxygen containing species at the three phase boundary;

FIG. 2 (FIGS. 2 a and 2 b) shows the known action of the partiallyblocking species at the three phase boundary;

FIG. 3 shows a block diagram of an example embodiment of the presentinvention;

FIG. 4 shows a block diagram of a further example embodiment of thepresent invention;

FIG. 5 (FIGS. 5 a and 5 b) shows block diagrams of example embodimentsof the present invention as applied to fuel cells;

FIG. 6 shows an example embodiment of an apparatus in accordance withthe present invention;

FIG. 7 shows an example embodiment of an electrode arrangement inaccordance with the present invention; and

FIG. 8 shows a further example embodiment of an apparatus in accordancewith the present invention.

DETAILED DESCRIPTION

The ensuing detailed description provides exemplary embodiments only,and is not intended to limit the scope, applicability, or configurationof the invention. Rather, the ensuing detailed description of theexemplary embodiments will provide those skilled in the art with anenabling description for implementing an embodiment of the invention. Itshould be understood that various changes may be made in the functionand arrangement of elements without departing from the spirit and scopeof the invention as set forth in the appended claims.

Example embodiments of the present invention have been found to enhancethe catalytic activity of prior art systems by a factor of 2 (andpossibly more) as a consequence of the action of a process called theDECAN process (Dynamic Enhancement of the Catalytic Activity atNanoscale), developed by Catelectric Corp., the assignee of the presentinvention.

Whereas the prior art NEMCA effect is essentially a DC phenomenon, theDECAN technology developed by Catelectric is built upon processes thatoccur under an alternating or variable current/voltage scheme.

The DECAN process provides a simple, real time way to control theenhancement of catalytic reactions. The DECAN process is described indetail in Applicant's commonly-owned U.S. Pat. No. 7,325,392, which isincorporated herein and made a part hereof by reference.

The real time control of the enhancement process in accordance with theexample embodiments of the present invention is essential for theefficient operation of an enhanced catalytic system. With Applicants'DECAN process, measurements sensed from the catalysts are fed into asimple electronic control module, which adjusts, also in real time, thepolarization state of the interface through the application ofalternating or variable voltages and currents.

Seetharaman et al., in an article entitled “Transient and PermanentEffects of Direct Current on Oxygen Transfer Across YSZ-ElectrodeInterfaces” [Journal of the Electrochemical Society, Vol. 144, no. 7,July 1997] (“Seetharaman”), identified and described a hysteresis effectat the three-phase boundaries in Pt/YSZ/gas environments, when theinterface transitions from a cathodic to an anodic current (see, e.g.,FIG. 8 of Seetharaman). The concentration of the oxygen-containing sitespresent at equilibrium can be modified by the passage of a cathodic oran anodic current, respectively. These changes have a dynamic effect onthe properties of the interface, as, for instance, on its catalyticproperties. The present invention achieves control of this hysteresiseffect through the real-time monitoring of certain electrical propertiesof the catalytic interface. These electrical properties are determinedas an average value over the whole interface involved in the catalyticprocess, and are therefore reflecting in real time the average catalyticactivity.

Seetharaman et al. assigned this hysteresis effect to the coexistence ofdifferent species, including species pumped electrochemically to or awayfrom the interface. Subsequent work [see, e.g., Seetharaman et al.,“Thermodynamic Stability and Interfacial Impedance of Solid-ElectrolyteCells with Noble-Metal Electrodes [Journal of Electroceramics, 3:3,279-299, 1999], has shown that this hysteresis is related to thetransient formation of partially blocking species at the charge transferinterface (the three phase boundary (TPB)) as illustrated in FIGS. 1 and2.

These species (e.g., oxygen-containing species (OCS)), are active in thecharge transfer and in the electrocatalytic reactions occurring at theTPB. When OCS is present at the TPB, it may block the reaction if it isinsulating with respect to ions as well as electrons (see FIG. 2 a).Electrically, the interface may be represented by a capacitor. On theother hand, the OCS may only be partially blocking. The OCS may then actas an intermediate step in the charge-transfer process (see FIG. 2 b).Such a result is likely if the OCS consists of oxygen loosely bonded tothe metal surface. In this case, the interfacial process is associatedelectrically with an impedance Z_(OCS) (referred to herein as“interfacial impedance”).

The magnitude of the interfacial impedance, Z_(OCS) depends on thestrength of the Metal-O bonds that need to be broken or established inthe oxygen-transfer process.

Therefore, the value of the interfacial impedance is directly related tothe concentration of the OCS, which, in turn, is related to theconcentration of the electrocatalytic sites at the interface.Accordingly, the values of the interfacial impedance for a given systemare therefore reliable indicators of the concentration of catalyticsites, which determines the rate of the reaction occurring at theinterface.

The correlation between the interfacial impedance and the yield of thecatalytic reaction is a complex function, which may be determinedexperimentally. In accordance with various embodiments of the presentinvention, the yield of the system can be maximized by a continuouscontrol of the NEMCA parameters by the alternating current applied tothe system (the pattern of change of the voltage and current density inthe time domain) and by monitoring the complex (AC) impedance of theinterface. This is the principle of the DECAN process of the presentinvention.

Various example embodiments of the present invention provide thecapability to force, enhance, and/or boost the reduction of NO_(x)(effectively controlling the pumping of the oxygen out of the NO_(x)molecular species) beyond the capability of the current state-of-the-artcatalytic systems. The pumping of oxygen away from the interfaceprovides also the reductive conditions necessary to nanotubes/fullerenedeposition.

Certain embodiments of the present invention also provide the capabilityto force, enhance, and/or boost the oxidation of CO to CO₂. As acorollary to the enhancement of the oxidation reactions, exampleembodiments of present invention provide the ability to oxidize carbonparticles (soot) to CO and subsequently to CO₂, resulting in a drasticdecrease (and possibly complete elimination) of soot particles from theDiesel exhaust gases. However, it has not yet been determined what willhappen with the other, minor components of the exhaust gases (inorganicash), which is not the focus of the present invention. However, thoseskilled in the art will appreciate that the addition of an electrostaticfilter downstream from the catalytic converter may provide one solutionfor dealing with these components. Such filters may be similar in designto those used in cement production.

Additionally, example embodiments of the present invention also enableregeneration of the catalyst in-situ, with a slight hysteresis.

Further, example embodiments of the present invention provide a built-insensing capacity for sensing the changes in the gas composition based onthe quantification of the trends in the subsets of a matrix of dataproviding the correlation between initial (pre-DECAN) gas composition ata given temperature, and the parameters of the DECAN process (real andimaginary components of the impedance, pattern of the application ofvariable voltage, pattern of the application of variable current, thepattern of the cross-correlation of the voltage and current (expressedby the matrix characterizing the vectorial product of the current andvoltage, which are complex quantities in the time domain). A FastFourier Transform FFT algorithm may be used to generate a syntheticcharacteristic based on the response of the gas composition to theapplied voltage/current, i.e., as a fingerprint of a change incomposition.

Polarization impedance is the difference between impedance measured atlow and high frequencies of alternating current. Polarization impedancecan be calculated according to the following formulas I and II:

i _(corr)=[β_(a)β_(c)/2.303(β_(a)+β_(c))][1/R _(p)]  (I)

R _(p) =|Z(jw)|_(w→0) −|Z(jw)|_(w→∞)  (II)

wherein i_(corr) equals a steady state corrosion current;β_(a) is the Tafel constant for an anodic reaction;β_(c) is the Tafel constant for a cathodic reaction;R_(p) is the polarization impedance (ohm);w=2×π×f wherein f is the frequency of the alternative current appliedand expressed in hertz (Hz);j is the imaginary unit number (−1)^(1/2);Z(jw) is the complex impedance of the interface as a function of thefrequency (ohm);(jw)|_(w→0) is the complex impedance of the interface when the frequencyapproaches zero (ohm); and(jw)|_(w→∞) is the complex impedance of the interface when the frequencyapproaches a very high frequency (ohm).

Test frequencies will vary depending on the characteristics andrequirements of the system, but suitable low frequencies typically rangefrom about 0.1 Hz to about 100 Hz and suitable high frequenciestypically range from about 10 kilohertz to about 5 megahertz.Polarization impedance is typically expressed in ohm. The method forcalculating polarization impedance is set forth in Applications ofImpedance Spectroscopy, J. Ross McDonald, p. 262, John Wiley & Sons(1987), which is incorporated herein by reference.

In the present control system, the polarization impedance generallycorresponds to the difference or drop in AC current across a catalystlayer/electroconductive support, which will vary in structure dependingupon the structure of the catalyst system. The difference in AC currentwill usually be between the first electrode/second electrode and the ACsensor. The polarization impedance is obtained when the impedance ismeasure at a low and a high frequency.

An example embodiment of a control system for controlling the DECANprocess in accordance with the present invention is shown in FIG. 3 andis generally referenced by the numeral 10. Control system 10 has anelectroconductive support 12 and a catalyst layer 14 situated thereon. Acurrent control unit 28 communicates with and controls and provides DCcurrent to a first electrode 17 and a second electrode 18 throughcurrent cables 20. First electrode 17 is contiguous to and in electricalcontact with electroconductive support 12. Second electrode 18 iscontiguous to and in electrical contact with catalyst layer 14. Currentcontrol unit 28 also controls and provides AC current to first electrode17 and second electrode 18 through current cables 22. A polarizationimpedance measurement unit 26 communicates with AC sensors 16, which arecontiguous to and electrical contact with catalyst layer 14 through datatransmission cables 24. Control system 10 also has a heater 36 and aheating control unit 34. Heating control unit 34 communicates withheater 36 through an interface 30 and a data transmission cable 24. Thecurrent control unit 28, polarization impedance measurement unit 26, andheating control unit 34 communicates with and are controlled by acentral processing unit 32 through interface 30. When control system 10is in operation, the process throughput such as a hydrocarbon stream orcombustion exhaust will contact catalyst layer 14 as it impinges orotherwise traverses it. Electrodes may take any electroconductive form,but usually take the form of an electrically conductive wire or conduitcontacting catalyst layer 14 or support 12.

FIG. 4 shows an alternate embodiment of a structure for implementing theDECAN process in accordance with the present invention. It should benoted that while certain of the layers 54, 56, and 58 shown in FIG. 4are required to reduce to practice the DECAN process in accordance withthe present invention, not all of them are necessary. For example, atleast two of these layers must be present. The remaining layer may bepresent or not, depending on the application of the invention or desiredresults.

FIG. 4 shows an electronic control device 50 capable of sending lowamplitude AC signals (in the frequency range 1 Hz to 500 kHz), and,simultaneously, DC signals (at voltages between +2 V and −2 V), as wellas low frequency (below 1 Hz), variable current and voltage. Theoperation of this electronic control device may be controlled by anexternally programmable control unit 52. The details of the softwaregoverning the operation of this programmable control unit are not thefocus of the present invention.

An underlying electronic conductor 54 may be provided having anelectrically contiguous/continuous phase. This material can be depositedon a sustaining insulating substrate, one example of which iscordierite. Other existing materials, or materials to be developed,having these properties may also be used with the present invention.Alternatively, this material can be a metallic member (a corrugatedstructure, a stack of sieves or any other structure with open,percolating channels, tortuous or not).

An electrically contiguous/continuous layer 56 of an ionic conductor(which may be any cationic or anionic material; such as Nafion-likematerials, stabilized zirconia, and others as is known in the art) mayalso be provided. This layer 56 can be deposited by washcoat-liketechniques, by CVD, by plasma-spraying, by electrophoresis, and or anyother suitable process leading to a thin film of catalyst deposited onthe conducting or semi-conducting substrate 54.

An electrically contiguous/continuous layer 58 of an electronic or ionicconductor (different from that of the previous layer 54 or 56) may alsobe provided. The ionic conductor of layer 58 may be any cation oranion-conducting material; such as Nafion-like materials, stabilizedzirconia, and others as is known in the art). The electronic conductorcan be a carbide, a doped oxide, doped silicon or any other conductingor semiconducting material, single-phase or mixed-phase. This layer 58may be deposited on top of the previous layer (either layer 54 or 56) byany of the techniques discussed above. The catalyst, as fine particles,is included in this layer 58, which comes in contact with the phasecarrying the substance(s) whose reaction is to be catalyzed.Alternately, the catalyst can be deposited on the surface of this layer58 which is exposed to the phase carrying the substance(s) whosereaction is to be catalyzed.

If the substrate of layer 54 is an electronic conductor (i.e., a metal),the layer 56 is not necessary, but may be present or useful in certainapplications of the present invention.

Conductors/electrodes 60, 62, and 64 may be provided for supplying theAC and DC current from the control device 50 to the layers 54, 56, and58, respectively.

In the example embodiment shown in FIG. 4, current/voltage are appliedbetween the layers 54, 56, and 58 in a three-terminal configuration, ina manner consistent with that described above in connection with FIG. 3.

It should be appreciated that FIG. 4 shows three layers 54, 56, and 58while FIG. 3 shows only an electroconductive support 12 and a catalystlayer 14. Further, it should be appreciated that the control device 50and programmable control unit 52 of FIG. 4 are equivalent to the controlunit 32 of FIG. 3. The remaining elements of FIG. 3, such as, forexample, the polarization impedance measuring unit 26, the currentcontrol unit 28, AC sensors 16, the heater 36, the heater control unit34, and interface 30, may also be used with the structure shown in FIG.4 to the same or nearly the same effect. In fact, where the substrate oflayer 54 of FIG. 4 is an electronic conductor and layer 56 is not used,the FIG. 4 embodiment becomes substantially similar to that of FIG. 3.

In an example embodiment of the present invention, an asymmetricalalternating current may be provided to the catalyst layer 58 (e.g., viaconductor 64). The polarization impedance of the catalyst layer may bemonitored (e.g., by polarization impedance measuring unit 26 asdiscussed above in connection with FIG. 3). The polarization impedancemay be controlled by varying the asymmetrical alternating currentsupplied to the catalyst layer 58 (e.g., by control unit 50). Thecontrol processes discloses in U.S. Pat. No. 7,325,392 (i.e.,controlling the catalytic enhancement via the values of the polarizationimpedance R_(p) (ohm)) can be applied to the oxidation of soot generatedby the operation of a diesel engine, or from incomplete combustion in acoal-operated heating installation (e.g., in a power plant). As usedherein the term “asymmetrical alternating current” is defined to mean analternating current whose amplitude of the positive part of the cycle(voltage or current) is different from the amplitude of the negativepart of the cycle (voltage or current), and can be defined by itsasymmetry factor. The asymmetry factor is the ratio of the largeramplitude of the cycle to the smaller amplitude of the cycle. The roleof the asymmetrical alternating current is to displace the migration ofthe interfacial charged species to/or away from the interface at thetime scales determined by the (variable) frequency of the asymmetricalalternating current.

In accordance with an example embodiment of the present invention, sootthat has built up on the catalyst layer may be eliminated. Inparticular, in such an example embodiment, carbon may be eliminated byforcing its oxidation through pumping oxygen from a substrate underDECAN conditions, or favoring the oxidation reaction under steamreforming conditions, in an excess of water. Sensing of the onset ofsoot deposition can be accomplished via examination of the matrix ofvalues of the interfacial impedance: such as, for example, the patternsof the change of the phase angle and of the polarization resistance,which tend to become indeterminate and scattered. The onset of thisscattering accompanies the onset of the carbon (soot) deposition, andcan be used as a trigger for the application of an example embodiment ofa soot oxidation scheme in accordance with the present invention.

Thus, in accordance with example embodiments of the present invention,oxygen may be provided the catalyst layer 58 to generate an oxidationreaction for eliminating carbon particles from the catalyst layer 58.Alternatively or additionally thereto, one of water and steam may beprovided to the catalyst layer 58 to enhance the oxidation reaction.

The catalyst layer 58 (together with layers 56 and/or layer 54) may beapplied to a catalytic reactor. The catalytic reactor may be builtaround a filter which retains the carbon particles. The deposition ofthe carbon particles on the catalyst layer 58 may be monitored. Themonitoring of the deposition of the carbon particles may comprisemonitoring at least one parameter which describes an interfacialimpedance of the catalyst layer 58 and determining an amount of thecarbon particles deposited on the catalyst layer as a function of valuesof the at least one monitored parameter. For example, the at least onemonitored parameter may comprise at least one of the monitoredpolarization impedance and a phase angle of the interfacial impedance.

Catalyst regeneration may also be achieved in accordance with an exampleembodiment of the present invention by utilizing a matrix of current andvoltage fluctuations, simultaneous (optionally) with a heating profile,which may all be monitored via the measurement of the R_(p) and phaseangle distribution. The effectiveness of the catalyst regeneration isevaluated by the value of the R_(p) (which has to return to a value asclose as possible to the value range characterizing the fresh, unusedcatalytic system) and the phase angle distribution (the phase angle hasto be as close to zero as possible). In other words, the polarizationimpedance will have a very low capacitive component; for example, phaseangle values between −5 degrees and +5 degrees will be consideredappropriate for catalyst regeneration within the scope of the presentinvention

Additional factors assisting in the regeneration of the catalyst may bewater vapor injection and the monitored variation of the partialpressure of oxygen in the carrier gas. Such variations in the partialpressure of oxygen can be achieved by methods well known in the priorart.

Thus, in accordance with example embodiments of the present invention,at least one of an amplitude and a phase of the asymmetrical alternatingcurrent may be varied (e.g., by control unit 50) in order to regeneratethe catalyst layer 58. For example, the at least one of the amplitudeand the phase of the asymmetrical alternating current may be varied tobring the polarization impedance to a value within a predetermined rangeof values when the polarization impedance value falls outside of thispredetermined range. This predetermined range may be a range of valuesaround an original polarization impedance value of the catalyst layer 58prior to use.

Further, the at least one of the amplitude and the phase of theasymmetrical alternating current may be varied to achieve a phase angleof an interfacial impedance of the catalyst layer 58 which is within arange of between approximately −5 degrees and +5 degrees.

In another example embodiment of the present invention, the applicationof at least one of water, oxygen, and heat to the catalyst layer 58 maybe controlled to enhance the regeneration of the catalyst layer 58.

Further, a partial pressure of oxygen in a carrier gas applied to thecatalyst layer 58 may be controlled (varied) in order to enhance theregeneration of the catalyst layer 58.

An alternate example embodiment of the present provides a further methodfor controlling a catalytic process. In such an example embodiment,monitoring a polarization impedance of the catalyst layer 58 ismonitored (e.g., using polarization impedance measuring unit 26).Additionally, at least one of an amount of water and an amount of oxygenapplied to the catalyst layer may be controlled.

In such an example embodiment, an alternating current may be applied tothe catalyst layer 58 and the polarization impedance may be controlledby varying the alternating current.

The method may further comprise varying at least one of a phase and anamplitude of the alternating current and/or controlling the at least oneof the amount of the water and the amount of the oxygen applied to thecatalyst layer 58 to provide at least one of oxidation of carbonparticles on the catalyst layer and regeneration of the catalyst layer58.

In addition, an amount of heat applied to the catalyst layer may becontrolled in order to further control the regeneration of the catalyst.The heat may be applied using heater 36 controlled by heater controlunit 34 (shown in FIG. 3), which may be responsive to control signalsfrom control unit 50.

The amount of the oxygen may be controlled by varying a partial pressureof oxygen in a carrier gas applied to the catalyst layer 58.

The deposition of the carbon particles on the catalyst layer 58 may bemonitored. The monitoring of the deposition of the carbon particles maycomprise monitoring at least one parameter which describes aninterfacial impedance of the catalyst layer 58 and determining an amountof the carbon particles deposited on the catalyst layer as a function ofvalues of the at least one monitored parameter. For example, the atleast one monitored parameter may comprise at least one of the monitoredpolarization impedance and a phase angle of the interfacial impedance.

In a further example embodiment of the present invention, the water maybe heated to generate steam. In such an example embodiment, thecontrolling of the amount of the water applied to the catalyst layer 58comprises controlling an amount of steam applied to the catalyst layer.

When regenerating the catalyst 58, the at least one of the amplitude andthe phase of the alternating current may be varied to return thepolarization impedance to a value within a predetermined range of valueswhen the polarization impedance value falls outside of thispredetermined range. The predetermined range may be a range of valuesaround an original polarization impedance value of the catalyst layer 58prior to use.

In addition, when regenerating the catalyst 58, the at least one of theamplitude and the phase of the asymmetrical alternating current may bevaried to achieve a phase angle of an interfacial impedance of thecatalyst layer which is within a range of between approximately −5degrees and +5 degrees.

In one example embodiment, the alternating current may comprise anasymmetrical alternating current.

The catalyst layer 58 may be applied to a catalytic reactor. Thecatalytic reactor may comprise a filter which retains the carbonparticles. If the catalytic reactor is built as a filter, this will makesure that the carbon-based particles are retained by the filter, andapproximately 98-99 mass % of the soot can be oxidized to CO2.

The controlling of the at least one of the amount of water and theamount of oxygen applied to the catalyst layer 58 may comprisecontrolling an amount of steam applied to the catalyst layer. The steammay be wet steam or dry steam, depending on the particular application.

The controlling of the amount of the oxygen applied to the catalystlayer 58 may comprise controlling environmental oxygen levels present inthe exhaust stream, for example by controlling an amount of water orsteam injected into the exhaust stream.

A local sensing function is provided in accordance with an exampleembodiment of present invention, which senses the matrix above,including the values of R_(p) and phase angle distribution (e.g., usingpolarization impedance measuring unit 26). The matrix is correlated withthe gas composition (for instance, the amounts of NOx, CO and othercomponents) and its variations. Brief (10⁻⁴−1 second) step functions ofapplied current/voltage between the working electrode (e.g., electrode64 of the catalyst 58 in FIG. 4) and the auxiliary electrode (e.g.,electrode 60 or electrode 62), followed by a Fast Fourier Transform(FFT) analysis of the pattern of the response of the polarized catalyticinterface measured between the working and the reference electrodes,provide a unique fingerprint, that can be assigned to a specificcomposition of the phase in contact with the catalyst. Thesecompositional changes can be relayed to the central computer thatcontrols the operation of the engine (i.e., an engine ECU), for thereal-time adjustment of the parameters controlling the operation of theengine: ignition parameters, valve timing, and the like. Thisapplication is not limited to the operation of Otto or Diesel engines;the operation of turbine engines can be controlled as well in accordancewith the composition of the exhaust gases.

This application does not require a separate sensor. The sensingfunction is performed by the hardware and the software described aboveand shown in FIGS. 3 and 4 (e.g., electronic control device 50,polarization impedance measuring unit 26).

With an example embodiment of the present invention, the functionalityof, for example, systems including multiple phase and/ormulti-functional catalysts, can be achieved by a system using only asingle-phase catalyst (built as described in connection with FIG. 4above), but on electrically separated substrates. Each electricallyindependent section of a stack can be polarized differently, and canthus be controlled to perform different functions (e.g., reduction ofNOx in one section, oxidation of carbon monoxide to carbon dioxide inanother section, or oxidation of unreacted hydrocarbons in a thirdsection).

Therefore, the same material can perform different functions indifferent areas of the catalytic reactor. This functionality can becombined with the sensing functions described in above. The externallyprogrammable control unit 52 (FIG. 4) can effect variations infunctionality from one area to another, as required.

The control methods discussed above can also be applied to control ofthe operation of fuel cells. Example embodiments of the presentinvention for controlling fuel cells in accordance with the presentinvention is shown in FIGS. 5 a and 5 b. It is known that the currentgenerated by a fuel cell 60 is maximized when the mass and chargetransfer across the MEA (membrane-electrode assembly) is maximized. Thepolarization resistance is minimized under these conditions. The fuelcell 60 of FIGS. 5 a and 5 b is shown as having an two catalyst layers66, an electrolyte layer 68 therebetween, and a respective catalystsupport 70.

In accordance with an example embodiment the present invention, for amaximum yield, a fuel cell 60 must be driven (any fuel cell type isincluded here) towards an operation scheme driven by the criterion ofminimizing the R_(p) and achieving a narrow phase angle distribution, asclose as possible to zero. FIG. 5 a shows an example embodiment of thepresent invention where the measurements and control of the fuel cellare carried out using a two electrode configuration(catalyst-to-catalyst layer) with a working electrode, WE andcounter-electrode, CE. FIG. 5 b shows an alternate embodiment of thepresent invention utilizing a four electrode configuration with twoelectrodes for each compartment, one electrode CE connected to thecatalyst layer, and the other electrode RE connected to the surface ofthe electrolyte membrane in direct contact with the environment of therespective compartment of the fuel cell.

In both of the above-described example embodiments, the signals fromelectrodes CE and RE are measured by an Electronic Control Device 62similar in function with that described above in connection with FIGS. 3and 4. The processing of the signal and the commands for driving theoperation of the fuel cell are functions which may be performed by aControl Unit 64 similar in function with that described above inconnection with FIG. 4.

When soot is deposited on the catalyst layer under an electric fieldduring the control processes described above (known as carbondeposition, which is undesirable, as discussed above), it was discoveredthat the deposited layer, which macroscopically looks like an amorphousblack powder, was found under electron microscopic examination topossess the structural characteristics of fullerenes and nanotubes, aswell as nanoparticles. It was further found that the growth of theindividual structured particles under the dominant electric field canlead to different types of deposits. In particular, it was found that ifone conducts a process under conditions known as conducive to carbondeposition, but also under using the DECAN process described above, theresult is an interfacial layer of nanotubes, fullerenes, and/ornanoparticles.

However, if the particles are not deposited under an electric field(e.g., with passive catalytic methods), they are just a mix of differenttypes of carbon, which cannot be separated from each other and areundesirable in catalytic systems because they obstruct the path ofreacting species to the catalytic sites.

Accordingly, in a further embodiment of the present invention, thecontrol processes described above may tailored to control thecharacteristics of the carbon particles deposited on the catalyst layer.For example, the control process may advantageously be used to depositcarbon particles on the catalyst layer in the form of carbon nanotubes,fullerenes, and/or nanoparticles. Accordingly, methods and apparatus forcontrolling the deposition of carbon particles on a catalyst layer arealso provided in accordance with the present invention.

In one example embodiment, a method for controlling a catalytic layerdeposition process is provided. As shown in FIG. 6, a feed stream 112containing a carbon source is provided to the catalyst layer 114. Anasymmetrical alternating current is provided (e.g., from electroniccontrol device 120) to a catalyst layer 114. A polarization impedance(R_(p)) of the catalyst layer is monitored. In order to monitor thepolarization impedance, the electronic control device 120 may includemeans for determining the applied current and voltage. The determinationof the polarization impedance from the sensed current is explained indetail in commonly-owned U.S. Pat. No. 7,325,392. Alternatively, thepolarization impedance may be monitored by polarization impedancemeasuring unit 26 as discussed above in connection with FIG. 3. Thepolarization impedance may be controlled by varying the asymmetricalalternating current from electronic control device 120. Controlling ofthe polarization impedance provides control over the structure andamount of carbon particles deposited on the catalyst layer 114 (in theform of a deposited layer 115).

The controlling of the polarization impedance may comprise correlatingthe time variation of the polarization impedance with the thickness andthe nature of the deposited layer 115. As an example, one practical wayto achieve this goal is to correlate the set of currently measured R_(p)values to a database 124 linking the polarization impedance value withdata regarding at least one of the chemical nature, structure andaverage value for ratios of deposit volume/unit of surface area, andadjusting the deposition and polarization conditions via a feedbacksystem/loop which may include electronic data evaluating the real timevariation of the value of the partial pressure of oxygen applied to thecatalyst layer 114. The oxygen may be applied to the carrier layer inthe form of a carrier gas 119 containing oxygen. The polarizationimpedance may be adjusted based on the monitoring of the partialpressure of oxygen in order to enhance the deposition of the carbonparticles on the catalyst layer. The determining of the partial pressureof oxygen may also be achieved via the electronic control device 120 asa function of a voltage measurement. For example, a monitoring of thepartial pressure of the oxygen may comprise monitoring an interfacialimpedance of the catalyst layer 114. The partial pressure of oxygen at alevel of the catalyst layer 114 may then be determined as a function ofthe interfacial impedance. Alternatively, the polarization impedance ofthe supported catalyst layer 114 may be monitored as discussed above,and the partial pressure of oxygen at the level of the catalyst layer114 may be determined as a function of the monitored polarizationimpedance (e.g., achieved via the electronic control device 120).

The catalyst layer 114 may be supported on or in close contact with asolid electrolyte (support 116). For example, the catalyst layer 114 maycomprise, platinum, semiconducting oxides, other semiconductingmaterials, etc., which are supported or are in close contact to a solidelectrolyte 116 (examples of solid electrolytes include, but are notlimited to: stabilized zirconia, stabilized bismuth oxide, differentforms of beta alumina, Nafion; and the like) or a mixed conductor.

In order to apply the alternating current to the catalyst layer 114,three electrodes may be provided as shown in FIG. 7. For example, areference electrode 140 may be applied to the solid electrolyte layer116, a counter electrode 142 may be applied to the solid electrolytelayer 116, and a working electrode 144 may be applied to the catalystlayer 114.

Experimentation has shown that carbon deposition occurs in such systemsas described above, under reducing conditions. Surprisingly, it wasfound that in the presence of a local electric field produced by thecontrol processes described herein, the product at the three-phaseinterface consists mostly or exclusively of carbon nanotubes,fullerenes, and/or nanoparticles from the deposited carbon particles.These deposits 115 can be visualized using, e.g., an electron microscopeand their structure can be determined using, e.g., electron diffractionor other adequate techniques.

The feed to the interface consists of at least the following components:

A) a feed stream 112 comprising a carbon source (e.g., a mix of CO, CO₂,hydrocarbons, oxygenated hydrocarbon-derivatives, organic compounds, andthe like, whether gaseous, or liquid); and

B) (optionally) a water or steam source (e.g., which may be included infeed stream 112 or separately provided in a secondary water or steamfeed 118), depending on the temperature at which the process isconducted.

The process may work in gas phase or in the liquid phase—the ionicconductivity of the solid electrolyte 116 appears to be a determiningfactor in this regard. The values of the ionic conductivity are situatedwithin the range of 1 to 10⁻⁴ ohm⁻¹*cm⁻¹ (most useful), but can besituated outside this range. The limits of the range depend on thespecific electronic equipment used for the measurement and the controlof the process.

In a further example embodiment as shown in FIG. 8, the feed stream 112may be introduced into a chamber 222 containing the catalyst 114. Thechamber 222 may comprise a tubular reactor. The alternating current maybe controlled by an electronic control device 120. The feed stream 112may be introduced to the chamber 222 from a tank 211. Water or steam 118may be introduced to the chamber 222 from a pump 217.

The method may further comprise extracting and/or electrically pumpingoxygen from the catalyst layer 114 (e.g., via pump 224) to generate areduction reaction for initiating or enhancing the deposition of carbonparticles 115 onto the catalyst layer 114.

The rate or structure of the carbon particles deposited on the catalystlayer 114 may be monitored (e.g., via the electronic control device120). The monitoring of the deposition of the carbon particles maycomprise monitoring at least one parameter which describes aninterfacial impedance of the catalyst layer 114 and determining anamount of the carbon particles 115 deposited on the catalyst layer 114as a function of values of the at least one monitored parameter. Forexample, the at least one monitored parameter may comprise at least oneof the monitored polarization impedance and a phase angle of theinterfacial impedance.

In a further example embodiment of the present invention, at least oneof an amplitude and a phase of the asymmetrical alternating current maybe varied by the electronic control device 120 in order to control thecharacteristics of the deposited layer 115. For example, the at leastone of the amplitude and the phase of the asymmetrical alternatingcurrent may be varied to bring the polarization impedance to a valuewithin a predetermined range of values when the polarization impedancevalue falls outside of this predetermined range. This predeterminedrange may be a range of values around an original polarization impedancevalue of the catalyst layer 114 prior to use (e.g., a clean catalystlayer).

Further, the at least one of the amplitude and the phase of theasymmetrical alternating current may be varied by the electronic controldevice 120 to achieve a phase angle of an interfacial impedance of thecatalyst layer 114 which is within a range of between approximately −10degrees and +10 degrees.

In another example embodiment of the present invention, the applicationof at least one of water, steam, oxygen, and heat to the catalyst layer114 may be controlled to control the deposition of the carbon layer onthe catalyst. For example, water or steam 118 may be introduced intochamber 222 via pump 217. Oxygen 119 may be introduced into chamber 222via pump 221. Heat may be applied to the catalyst layer 114 via aheating element 234 controlled by a temperature control unit 236.

Further, a partial pressure of oxygen in a carrier gas 119 applied tothe catalyst layer 114 may be controlled (varied) in order to enhancethe deposition of carbon on the catalyst layer.

The method may further comprise varying at least one of a phase and anamplitude of the alternating current and/or controlling the at least oneof the amount of the water, steam, and/or oxygen applied to the catalystlayer 114 or deposited layer 115 to provide at least one of a reductionof at least one of the liquid phase and the gas phase in contact withthe catalyst layer 114, and to stimulate growth of the deposited layer115.

In addition, an amount of heat applied to the catalyst layer may becontrolled (e.g., via temperature control unit 236) in order to furthercontrol the structure and/or thickness of the deposited layer 115.

In a further example embodiment of the present invention, the water maybe heated to generate steam. In such an example embodiment, thecontrolling of the amount of the water applied to the catalyst layer 114may comprise controlling an amount of steam applied to the catalystlayer 114.

The method may further comprise harvesting nanotubes, fullerenes, and/ornanoparticles from the deposited carbon layer 115. For example, thedeposition interface can be viewed as a filter, and the nanotubes,fullerenes, and/or nanoparticles can be removed from the filter usingknown chemical engineering methods for removing valuable precipitatesfrom a filter (for example, vibratory removal, removal with the help ofa fluid phase (e.g., water introduced from pump 217) which washes thedeposits 115 into a suitable particulate filter 226, and the like).

After harvesting of the nanotubes, the catalyst layer 114 may beregenerated as discussed above.

The present invention may also be expanded to control deposition ofnanotubes, fullerenes, or nanoparticles made from other materials ofelectronic interest (e.g., silicon/doped silicon, silicon carbide,gallium arsenide, niobium, boron and the like).

It should now be appreciated that the present invention providesadvantageous methods and apparatus for controlling catalytic processes,including soot elimination, catalysts regeneration, and carbondeposition in the form of carbon nanotubes, fullerenes, and/ornanoparticles.

Although the invention has been described in connection with variousillustrated embodiments, numerous modifications and adaptations may bemade thereto without departing from the spirit and scope of theinvention as set forth in the claims.

1. A method for controlling a catalytic layer deposition process,comprising: providing a feed stream comprising a carbon source to acatalyst layer; providing an asymmetrical alternating current to thecatalyst layer; monitoring a polarization impedance of the catalystlayer; and controlling the polarization impedance by varying theasymmetrical alternating current; wherein the controlling of thepolarization impedance provides control over the structure and amount ofcarbon particles deposited on the catalyst layer.
 2. A method inaccordance with claim 1, wherein the controlling of the polarizationimpedance further comprises correlating a time variation of thepolarization with at least one of a thickness and the structure of thedeposited carbon particles on the catalyst layer.
 3. A method inaccordance with claim 2, wherein: measured polarization impedance valuesfrom said monitoring are correlated to a database linking each of thepolarization impedance values with data regarding at least one of thechemical nature, structure and average value for ratios of depositvolume/unit of surface area.
 4. A method in accordance with claim 3,further comprising: applying a carrier gas containing oxygen to thecatalyst layer; monitoring a partial pressure of oxygen in the carriergas at the catalyst layer; adjusting the polarization impedance based onthe monitoring of the partial pressure of oxygen in order to enhance thedeposition of the carbon particles on the catalyst layer.
 5. A method inaccordance with claim 1, wherein the catalyst layer is supported on orin close contact with a solid electrolyte.
 6. A method in accordancewith claim 5, wherein an ionic conductivity of the solid electrolyte iswithin a range of between approximately 1 to 10⁻⁴ ohm⁻¹*cm⁻¹.
 7. Amethod in accordance with claim 5, wherein: the catalyst layer comprisesone of platinum, a semiconducting oxide, a semiconducting materials; andthe solid electrolyte comprises one of stabilized zirconia, stabilizedbismuth oxide, forms of beta alumina, Nafion, or a mixed conductor.
 8. Amethod in accordance with claim 1, wherein the carbon deposits compriseat least one of nanotubes, fullerenes, and nanoparticles.
 9. A method inaccordance with claim 8, further comprising: harvesting said at leastone of nanotubes, fullerenes, and nanoparticles from the depositedcarbon particles.
 10. A method in accordance with claim 9, furthercomprising: varying at least one of an amplitude and a phase of theasymmetrical alternating current in order to regenerate the catalystlayer subsequent to said harvesting.
 11. A method in accordance withclaim 1, wherein the carbon source comprises at least one of CO, CO₂,hydrocarbons, oxygenated hydrocarbon-derivatives, and organic compounds.12. A method in accordance with claim 11, wherein the feed streamfurther comprises one of water or steam.
 13. A method in accordance withclaim 1, further comprising: one of extracting or electrically pumpingoxygen from the catalyst layer to generate a reduction reaction forinitiating or enhancing the deposition of the carbon particles onto thecatalyst layer.
 14. A method in accordance with claim 1, furthercomprising: monitoring deposition of the carbon particles on thecatalyst layer.
 15. A method in accordance with claim 14, wherein themonitoring of the deposition of the carbon particles comprisesmonitoring a rate or structure of the carbon particles deposited on thecatalyst layer.
 16. A method in accordance with claim 14, wherein themonitoring of the deposition of the carbon particles comprises:monitoring at least one parameter which describes an interfacialimpedance of the catalyst layer; and determining an amount of the carbonparticles deposited on the catalyst layer as a function of values of theat least one monitored parameter.
 17. A method in accordance with claim16, wherein the at least one monitored parameter comprises at least oneof the monitored polarization impedance and a phase angle of theinterfacial impedance.
 18. A method in accordance with claim 1, furthercomprising: varying at least one of an amplitude and a phase of theasymmetrical alternating current in order to control characteristics ofthe deposited layer.
 19. A method in accordance with claim 18, whereinthe at least one of the amplitude and the phase of the asymmetricalalternating current is varied to bring the polarization impedance to avalue within a predetermined range of values when the polarizationimpedance value falls outside of the predetermined range.
 20. A methodin accordance with claim 19, wherein the predetermined range comprises arange of values around an original polarization impedance value of thecatalyst layer prior to use.
 21. A method in accordance with claim 18,wherein the at least one of the amplitude and the phase of theasymmetrical alternating current is varied to achieve a phase angle ofan interfacial impedance of the catalyst layer which is within a rangeof between approximately −10 degrees and +10 degrees.
 22. A method inaccordance with claim 1, further comprising: applying at least one ofwater, steam, oxygen, and heat to the catalyst layer; and controllingthe application of the at least one of the water, steam, oxygen, andheat in order to control the deposition of the carbon particles on thecatalyst layer.
 23. A method in accordance with claim 1, furthercomprising: applying a carrier gas containing oxygen to the catalystlayer; and controlling the partial pressure of oxygen in the carrier gasin order to enhance the deposition of the carbon particles on thecatalyst layer.
 24. A method in accordance with claim 1, wherein thefeed stream may comprise at least one of a liquid phase and a gas phase.25. A method in accordance with claim 24, further comprising at leastone of (a) varying at least one of a phase and an amplitude of thealternating current, and (b) controlling at least one of an amount ofwater, steam, and oxygen applied to the catalyst layer or to a depositedlayer formed by the deposition of the carbon particles in order toprovide at least one of (i) a reduction of the at least one of theliquid phase and gas phase in contact with the catalyst layer, and (ii)stimulate growth of the deposited layer.
 26. A method in accordance withclaim 24, further comprising: controlling an amount of heat applied tothe catalyst layer in order to further control at least one of thestructure and a thickness of the deposited carbon particles on thecatalyst layer.
 27. A method for controlling a catalytic layerdeposition process, comprising: providing a feed stream to a catalystlayer, the feed stream comprising at least one of carbon, silicon, dopedsilicon, silicon carbide, gallium arsenide, niobium, and boron;providing an asymmetrical alternating current to the catalyst layer;monitoring a polarization impedance of the catalyst layer; andcontrolling the polarization impedance by varying the asymmetricalalternating current; forming a deposition layer on the catalyst layer asa function of the controlling of the polarization impedance; wherein thedeposition layer comprises at least one of nanotubes, fullerenes, andnanoparticles.
 28. Apparatus for controlling a catalytic layerdeposition process, comprising: means for providing a feed streamcomprising a carbon source to a catalyst layer; means for providing anasymmetrical alternating current to the catalyst layer; means formonitoring a polarization impedance of the catalyst layer; and means forcontrolling the polarization impedance by varying the asymmetricalalternating current; wherein the controlling of the polarizationimpedance provides control over the structure and amount of carbonparticles deposited on the catalyst layer.